[Purposes]The paper aims to compare and study the purification effect and mechanism of various emergent plants on total nitrogen and ammonia nitrogen in sewage[Methods]Six types of emergent plants, including Oenanthe javanica(Bl.)DC., Houttuynia cordata thunb, Thalia dealbata Fraser, Cyperus alternifolius(L.) Rikli,Arundo donaxvar. versicolor and Vetiveria zizanioides (L.)Nash, were selected, through outdoor greenhouse soilless hydroponic planting test, the content of total nitrogen and ammonia nitrogen, pH, DO of the four types of sewage, plant physiological indicators and environmental temperature were tested regularly. [Findings]① During the first 14 d of the test,the removal rate of ammonia nitrogen and total nitrogen in sewage increases rapidly, and on the 21st day,the increase rate slows down,and on the 28th day,a certain degree of rebound occurs in some parts.After that, it fluctuates until basically stable. ② As the concentration of sewage increases, the ability of plants to remove nitrogen also increases. The metabolic capacity and growth trend of plants are positively correlated with the ability of plants to remove nitrogen. ③ The pH of the experimental sewage drops.Among them,the pH of these wage in the potted plant system of Thalia dealbataFraser has the largest decrease, and the correlation between the concentration of the sewage and the change of pH is not obvious. The content of DO has certain fluctuations, but the water environment is basically oxidized. Among all kinds of plants, the content of DO in the experimental sewage of Arundo donaxvar. versicolor and Thalia dealbata Fraser is relatively higher. [Conclu-sions]The growth needs of plants and the microbial activities of plant roots are the main mechanisms for emergent plants to purify nitrogen in water bodies. Catalase activity,root vitality and plant growth are positively correlated with the ability of plants to purify nitrogen pollution in water bodies. It is recommended that Arundo donax var. versicolor and Thalia dealbata Fraser be selected as the first emergent plants to treat nitrogen-polluted sewage in wetland system construction in SouthChina.